Streaming-media technologies serve on-demand and live video for corporate communications, promotion, sales and training. How tightly the video codecs compress video data for transmission dictates the streaming bandwidth requirements. Codecs with tight compression algorithms, such as RealNetworks' RealMedia, use as little as 20 Kbps of bandwidth. But high-quality video and other corporate LAN communications generally use MPEG standards for MPEG-1 and MPEG-2. This quality ranges from 30 frames per second for full-motion video to 60 interlaced fields per second to accommodate broadcast video.

MPEG-1 can take up to 1.5 Mbps per stream. MPEG-2 generally requires 2 Mbps to 6 Mbps but can need as much as 40 Mbps. MPEG-4 calls for less than its predecessors and targets the low bandwidth requirements on the Internet along with Apple Computer, Microsoft and RealNetworks. It needs 64 Kbps to 4 Mbps.

Traffic Prioritization

Bandwidth alone won't ensure the smooth delivery of real-time voice and video packets, especially considering IP's best-effort nature over Ethernet. You'll likely need additional guarantees under heavy loads, so consider upgrading to Layer 3 switches and traffic prioritization strategies such as RSVP (Resource Reservation Protocol), DiffServ (Differentiated Services) and MPLS (Multiprotocol Label Switching).

RSVP is designed to clear a path for audio and video traffic to reduce packet delay and loss. This flow-based communication protocol, which signals a switch or router to reserve bandwidth for a real-time transmission, such as a VoIP (voice over IP) call, allows a node to specify an end-to-end delay, such as 100 ms.

RSVP does not scale well, however, as every device along the path from packet origin to destination needs to maintain the state of the connection. Therefore, small to midsize enterprises can benefit from RSVP; large enterprises must discriminate services without maintaining a per-flow state at every switch. QoS strategies such MPLS and DiffServ will likely be more suitable.

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Implementing QoS with MPLS is like building a circuit-switched network that can create end-to-end circuits over any type of Layer 2 transport medium. In an MPLS network, a LER (Label Edge Router) assigns incoming packets a "label." Packets then travel along an LSP (Label Switch Path) that makes forwarding decisions based on the label's contents. At each hop along the path, an LSR (Label Switch Router) strips off the existing label and applies one with new forwarding instructions. Network operators establish LSPs to route around network congestion or create IP tunnels for network-based VPNs.

MPLS standards are still advancing through the IETF, and implementations have evolved differently, depending on the vendor. For example, Cisco Systems implements MPLS as Tag Switching. If you standardize on routers and switches from Cisco or another vendor that supports MPLS, your voice and video traffic will get priority without RSVP's heavy overhead. In addition, some private network providers, such as Masergy Communications, employ MPLS to move converged traffic to your remote offices.

If your enterprise is not a Cisco or Extreme Networks shop and you have heterogeneous networking equipment, you can use a QoS option such as DiffServ. Layer 3 switches (ASIC-based routers) can now perform route lookups at sufficient speeds to obviate label switching. Rather than tag traffic the way MPLS does, DiffServ modifies bits in the IP header to indicate QoS. DiffServ-compliant switches, such as Extreme Networks' Summit and BlackDiamond devices, read the value stored in the IPv4 packet header's ToS (Type of Service) or IPv6 packet's Traffic Class octet.

The value or DSCP (Differentiated Services Code Point) is 6 bits wide and capable of 64 classifications. The default code point (000000) represents a common IP packet and maintains IP's best effort in forwarding. Code points for preferential treatment (11x000) are given priority queuing and can be forwarded using a variety of mechanisms (such as strict priority queuing, weighted fair queuing and class-based queuing).

Although DiffServ may appear to be the QoS of choice for large enterprises, you need to test this solution in your environment. For example, vendors may use different forwarding mechanisms for the same DSCP. Other environments with Gigabit Ethernet backbones may have little need for QoS on the LAN, but may need to prioritize traffic over a saturated T1 WAN link. In that case, both a QoS strategy and a packet shaper, such as Packeteer's PacketShaper, may provide the requisite assurances that voice and video traffic will receive priority throughout the enterprise.

Tools such as NetIQ Corp.'s Vivinet Assessor can analyze enterprise environments and traffic patterns and assess the impact of voice traffic, using codecs such as G.711. In the future, such tools will evaluate the impact of video traffic.