Load Balance Voice Over IP SIP traffic in your BladeCenter economically and efficiently
with the Layer 2-7 Gigabit Ethernet Switch modules from BLADE Network Technologies.
Voice over IP- Session Initiation Protocol (SIP)
Load Balancing in the IBM BladeCenter
Solution Brief
Introduction
The convergence of voice and data applications over the IP network means that time- and latency-sensitive applications for voice and video have become dependent on the services of traditional IP networks to carry their traffic. Networks must be robust and provide
uninterrupted service for these applications. The quality, reliability, and thus the reputation of applications such as Voice over IP and video conferencing depends largely on whether the IP networks they run on can provide prioritized service, low latency and high availability to ensure a quality experience. Connections that fail or are rerouted to another server either in the same or in another network must be handled transparently with no discernable impact to the user.
Session Initiation Protocol (SIP) is the protocol that provides the framework for application such as IP telephony (Voice over IP), and Instant Messaging. This brief examines how SIP traffic can be managed for optimal connectivity, persistence, high availability, and security through use of a Layer 2-7 switching technology in the IBM BladeCenter. SIP application servers resident on BladeCenter server blades can realize optimal performance from the load balancing, high availability, global server load balancing, and security features available in a Layer 2-7 blade switch.
Requirements
Flexible and Upgradeable
Infrastructure
The cumulative spending forecast for networking equipment, software and professional services for IP-based telecommunications technology is expected to reach nearly $13 Billion from 2006 to 2010.i
Deployment of voice over IP solutions are ideally matched to the blade server environments. Blade server systems are the fastest growing segment of the server market by form factor ii and their flexibility allows for rapid upgrades of equipment and software using off the shelf technology. An open blade server architecture as found in the IBM BladeCenter enables commercial off the shelf products to be installed onto a blade server easily and without code modifications.
Application Load balancing at layer
4-7
Any server, regardless of its form factor or application, is limited in the number of concurrent connections and sessions it can handle at any given time. Servers must operate at their optimal capacity, and traffic load-balanced amongst multiple servers for ideal network performance.
Individual SIP servers have limited scalability. In order to maximize scalability and availability, application servers should be load balanced and client to server sessions should be maintained. Load balancing is achieved by assigning the servers a virtual IP address. Client requests to real servers are intercepted by the application switch’s virtual IP address, and load balancing metrics assigned on the switch determine how traffic is to be distributed.
When a new session is established, the switch directs client traffic to a server based on server availability and routes new sessions to a server. A mathematical hashing function within the load balancing metric, combined with a session entry in a session table, ensures that subsequent sessions from the same client are routed to the same server.
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Session Persistence
Session persistence increases efficiency of server responses. When repeated requests from the same client are sent to the same server, information stored in the server’s short-term cache memory can be accessed with much greater efficiency than if a server has to send those requests out to cache servers located elsewhere on the network. For example, SIP server queries to the home subscriber server (HSS) can be cached in local server memory. By providing client persistence to the same server, the BNT Layer 2-7 GbESM increases the efficiency of SIP server response.
VOIP Application Performance
For systems running VOIP applications, the blade servers must not become overloaded by distributing the incoming calls. An imbalance of overloaded and under loaded servers results in dropped calls, jittery voice quality, or service interruptions. VOIP applications must remain available to users during periods of peak call volume. Incoming calls must be redirected if a server reaches peak capacity, or if a link fails, or if a server has been attacked.
VOIP applications are also extremely time-sensitive--VOIP traffic must be guaranteed high priority using Quality of Service in order to minimize latency and maintain call quality.
Session Initiation Protocol
Typically most VOIP sessions are initiated through the Session Initiation Protocol (SIP), which is an application-level control protocol for Internet multimedia conferencing, telephony, event notification and instant messaging. Defined as RFC 3261 by the Internet
Engineering Task Force (IETF), SIP protocol initiates call setup, routing, authentication and other feature messages to endpoints within an IP domain.
SIP protocol performs the following functions: locate users (callers and called parties) determine user capability (what type of protocol (TCP, UDP) and other capabilities the user can support)
determine user availability
determine call setup (how to create the call)
determining call handling (how to keep the call up and how to bring the call down)
The Solution
BNT Layer 2-7 Gigabit Ethernet
Switch Module for IBM BladeCenter
The BNT Layer 2-7 Gigabit Ethernet Switch Module (GbESM) for IBM BladeCenter is a high performance application switch that performs at wire speed at Layer 2 through Layer 7, and delivers more than 60% better Layer 4 session performance than using an external Layer 4-7 switch, and offers a 60% price-performance advantage over a blade server with integrated layer 2 and external Layer 3-7 switching.iii The BNT Layer 2-7 GbESM
inserts into networking bays with the IBM BladeCenter chassis. Capable of handling 28,000 SIP session setups and teardowns per second, the BNT Layer 2-7 GbESM and is an ideal candidate for small and medium sized businesses (SMB) wishing to implement VOIP in IBM BladeCenter. Each switch is capable of up to 36 Gbps of full-duplex bandwidth per switch, and can handle up to 150,000 concurrent SIP sessions. iv
SIP Load Balancing
Cost-effective SIP load balancing of SIP proxy servers in the IBM BladeCenter can be achieved using BNT Layer 2-7 GbESM switch modules. Compatible with IBM BladeCenter, BladeCenter T, BladeCenter H or BladeCenter HT, the BNT Layer 2-7 GbESM is an excellent alternative to more expensive external load balancers or other NAT devices.
Session Initiation Protocol (SIP) load balancing on the BNT Layer 2-7 GbESM can function with any SIP server that uses shared or clustered databases to share signaling data for registration and invites.v A pair of Layer 2-7 GbESMs per chassis can provide high availability and perform application-intelligent switching for up to 64 virtual servers for up to 256 virtual services including SIP.
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Stateful Inspection
The BNT Layer 2-7 GbESM performs stateful inspection of SIP messages to scan and hash calls based on a SIP Call-ID header destined for a SIP server. Stateful inspection means that a packet is inspected not only for its source and destination information found in the header, but also packet contents found at Layer 7 (the application layer). Once the switch has identified the Call-ID which identifies a specific SIP session, it sends future messages from the same Call-ID to the same SIP server.
UDP-based Load Balancing
Voice protocols use both control (RTP/RTCP) and signaling (SIP) channels for each call. Voice content is carried over RTP/RTCP, which runs on dynamically generated UDP port numbers.
Session Persistence
Once a SIP session has been established between the client and SIP server, the BNT Layer 2-7 GbESM will maintain a persistent session so that the call originating from the same client IP address will always go to the server with the established session. As noted above, session persistence is established from the first client-to-server connection by means of the mathematical hash in the load balancing metric. This hashing function determines which server should receive the connection, and then records an entry in the GbESM’s session table. Subsequent requests from this client bypass the load balancing metric as the switch directs the connection to the server recorded in the session table.
SIP Health Checks
The BNT Layer 2-7 GbESM can perform a SIP-specific application health check on real servers based on SIP requests and responses. Some of the responses SIP health check monitors are shown in the table below:
SIP Response Message Types
Description
1xx Information Responses – For Example: 180, Ringing 2xx Successful Responses – For
Example: 200, OK
3xx Redirection Responses – For Example: 302, Moved Temporarily
4xx Request Failures Responses – For Example: 403,
Forbidden
5xx Server Failure Responses – For Example: 504, Gateway Time-out
6xx Global Failure Responses – For Example: 600, Busy Everywhere
For SIP register health checks, the BNT Layer 2-7 GbESM sends a SIP REGISTER request to the configured server(s). The switch looks for server response message type ―1xx‖, ―2xx", "3xx" or "4xx" to determine if the server is UP. If the switch receives a response message type 2xx, 3xx or 4xx the server(s) are declared as ―UP‖. If switch receives a type "5xx" or "6xx" response the switch will declare the server(s) as ―DOWN‖. If after 3 register requests the switch does not receive any response back from the server(s), the switch will mark the server(s) as ―down.‖
Network Address Translation
Network Address Translation is an Internet standard implemented on the BNT Layer 2-7 GbESM, which maps external IP addresses outside the network, to hidden internal IP addresses. The BNT Layer2-7 GbESM performs deep packet inspection and changes the private addresses of Media Portal Servers in the SDP/RTP packet to the advertised Public address to avoid ―one way‖ speech problems.
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Traffic Prioritization
The Layer 2-7 GbESM software includes rate limiting based on Quality of Service Access control lists (IP ACLs or MAC ACLs), class maps, and policy maps which guarantee highest
priority for SIP traffic and minimize dropped packets.
High Availability
In addition to optimizing the load on multiple SIP servers in an IBM BladeCenter, the BNT Layer 2-7 GbESM can ensure high availability at Layer 2, Layer 3, and Layer 4.
Layer 2 Trunk Failover - At Layer 2, network adapter teaming on the blade servers, combined with Layer 2 Trunk Failover on the BNT Layer 2-7 GbESM can be enabled on any switch trunk group. If any of the links in a trunk fail, the switch triggers the Network Interface Card (NIC) team on the affected server blades to failover from the primary to the backup NIC. This feature can also be enabled to detect failover for links within a VLAN, and enable/disable service to VLANs. Virtual Router Redundancy Protocol - At Layer 3, Virtual Router Redundancy Protocol (VRRP) enables redundant router configurations within a LAN, providing alternate router paths for a host to eliminate single points-of-failure within a network. VRRP ensures that if the master switch fails, traffic will be rerouted through the backup switch. In high availability environments where the backup switch takes over when a master fails, all the SIP sessions on the master switch are reestablished on back up switch.
Active-Active Redundancy - In order to minimize the possibility of complete session failover on a switch, Active-Active
redundancy, using BLADEOS Layer 4 extension to VRRP, can provide redundancy for virtual services such as SIP, HTTP, FTP). In Active-Active redundancy, a pair of BNT Layer 2-7 GbESMs remains active and provides failover for one another at the same time on different virtual server IP addresses (VIPs), resulting in higher capacity and performance than when the switches are used in an Active-Standby configuration. For example, each Layer 2-7 GbESM is configured with two VIP
addresses for load balancing SIP traffic.
Switch 1 is configured with VRRP to be the Active (master) switch for VIP address 1, and the Standby (backup) switch for VIP 2. Switch 2 is configured as the Standby on VIP address 1 and Active (master switch) on VIP address 2.
Content-Intelligent Security
Advanced Denial of Service Attack Prevention - Many types of cyber-attacks have exploited the weaknesses of traditional firewalls, which allow or deny traffic by opening or closing certain service ports, such as HTTP port 80. Absent a better security method, malicious content can pass through these well-known service ports. The BNT Layer 2-7 GbESM can protect SIP severs by performing deep packet inspection to block any malicious content before it is sent to the real servers.vi Protection against UDP Blast Attacks - Malicious attacks over UDP protocol ports are becoming a common way to bring down real servers. The switch can be configured to restrict the amount of traffic allowed on any UDP port, thus ensuring that backend servers are not flooded with data.
UDP Pattern Matching - For SIP protocol, which is UDP-based, the switch can be configured to examine a UDP packet from either the beginning, from a specific offset value (starting point) within the packet, and/or from a specified depth (number of characters) into the packet. If an offending pattern is matched, the switch will drop those packets.
Site Availability: Global Server Load
Balancing
Geographically redundant sites ensure the availability of key applications and minimize service outages in the event of a natural disaster or other catastrophe. The BNT Layer 2-7
GbESM can load balance traffic both locally and across multiple sites and domains.
The Global Server Load Balancing (GSLB) feature performs or initiates a global server selection to direct client traffic to the best server for a given domain during the initial client connection. GSLB ensures that if all connectivity within a BladeCenter fails, user sessions can be redirected to another BladeCenter chassis in another location and domain. Based on DNS
5 name resolution of SIP URIs, GSLB redirects client sessions to another GSLB-enabled site based on site health, site proximity to the client, and the response time required to retrieve content.
Conclusion
Deployment of voice over IP solutions using the Session Initiation Protocol (SIP) are increasingly migrating to blade servers due to the flexibility, scalability and performance advantages inherent in the bladed environment. IBM is the only blade server system vendor with integrated Layer 2-7 switching. IBM BladeCenter customers have the unique opportunity to take advantage of the content-intelligence, application load balancing, security, availability and price performance benefits of the BNT Layer 2-7 GbESM for optimal SIP application performance and availability, while reducing infrastructure and deployment costs.
Equipment List
Infrastructure
2 IBM BladeCenterE/H/S/T/HT Chassis 2 BNT Layer 2-7 Gigabit ESMs
14 IBM blade serves running commercial off the shelf SIP server software
14 PCI side cards (optional) for connectivity to Public Switches Telephone Network (PSTN) VOIP
Standard server software as recommended by your vendor Standard client software as recommended by your vendor
N – IP enabled terminals/phones
About BLADE Network Technologies
BLADE Network Technologies is the leading supplier of Gigabit and 10G Ethernet network infrastructure solutions that reside in blade servers and ―scale-out‖ server and storage racks. BLADE’s new ―virtual, cooler and easier‖ top-of-rack switches demonstrate the promise of ―Rackonomics‖—a revolutionary approach for scaling out data center networks to drive down total cost of ownership. The company’s customers include half of the Fortune 500 across 26 industry segments, and an installed base of over 250,000 network switches connecting more than 2,000,000 servers and over 5 million switch ports.
i Doyle, Lee, and Bozman, Jean: ―The Benefits of Blade Servers in Telecommunications IT and Network Infrastructure,‖ IDC Whitepaper #205415, Feb 2, 2007.
ii Ibid.
iii, ―IBM eServer BladeCenter with Nortel Networks Layer 2-7 Gigabit Ethernet Switching Module: Price/Performance of Integrated vs. External Switching,‖ Tolly Group, No 204104, January 2004.
iv The actual performance will vary depending on the number of SIP servers and their capacity. v Nortel MCS (Multimedia Communications Server), Commmunigate Pro and Cisco are examples of SIP servers with synchronized databases. However, this does not constitute a product recommendation by BLADE Network Technologies or IBM. vi This feature can be useful as an emergency fix during early stages of a virus attack, and is designed to function as a supplement, not a replacement for more advanced content-aware firewalls on the network.
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BNT Layer 2-7 GbESM Details
Major Applications
Server load balancing Local server load balancing
Global server load balancing Application health checks SIP, IP, LDAP, DNS, RTSP and others
Network device load balancing
VPN
Intrusion detection Uplink to Core Routing Infrastructure WAP gateway Application redirection and
load balancing
SSL persistence Cache
Streaming media
Content Intelligence Layer 7 inspection
Cookie, URL, HTTP header, user agent
Embedded security services Access control
Denial of service attach
Technical Specifications
Total ports: 20 4 External 10/10/100 Mbps
14 internal 1000 Mbps 2 Management (internal) 100Mbps
Layer 2 & 3 throughput Line rate
Concurrent Sessions 300,000
Layer 4 sessions/second Up to 64,000 (with zero session loss)
Layer 7 sessions/second Up to 28,000 (with zero session loss)
IP routing interfaces 128
Virtual service support 256
Real server support 64
Policy filters 1,024
VLANs 128
Default gateways 255
Trunk groups (for external ports)
2
Network protocol & standards compatibility
10Base-T/100Base-TX/1000 Base-TX
EEE 802.3 - 2000
Spanning Tree EEE 802.1d
Logical link control EEE 802.2
Flow control EEE 802.3x
Link negotiation EEE 802.3z
VLANs EEE 802.1Q
Frame tagging on all ports when VLANs enabled
EEE 802.1Q
SNMP support FC 1213 MIB-II, RFC 1493
Bridge MIB, FC 1398 Ethernet-like MIB, RFC 1757 RMON1 (groups 1-4), and RFC 1573 MIB compliant. Alteon Enterprise MIB Denial of service attack
prevention
IP ACLs
Protection against common DoS attacks
Protocol-based rate limiting UDP Blast Attack Prevention TCP or UDP pattern matching
©2009 BLADE Network Technologies, Inc. All rights reserved. Information in this document is subject to change without notice. BLADE Network Technologies assumes no responsibility for any errors that may appear in this
document. All statements regarding BLADE’s future direction and intent are subject to change or withdrawal without notice, at BLADE’s sole discretion. http://www.bladenetwork.net. MKT080925
