Using PCoIP® Zero Clients with PCoIP Host Cards
T E C H N I C A L N O T E S / 1 2
3.4 Packet Loss
Typical symptoms of packet loss include sluggish desktop responsiveness and blurry images. Packet loss can
aect both the user experience and USB connectivity even if the base latency and bandwidth meet PCoIP
protocol requirements. Packet loss below 0.1% should not have a noticeable impact on user experience or USB
connectivity.
While network packet loss is usually specified as a percentage (e.g., 0.1%), physical networks typically lose
packets in small bursts rather than being randomly dispersed throughout time. However, if a network is
experiencing random, persistent packet loss, the PCoIP protocol will interpret this as network congestion and
reduce the bandwidth it transmits in an attempt to eliminate this “phantom” congestion. Since the persistent
packet loss is coming from the network itself rather than from congestion, the PCoIP session eventually reaches
the “floor” bandwidth (Device Bandwidth Floor, Section 3.1.2) and will result in a lower level of experience than
the network can support.
Note: Many “WAN emulators” simulate packet loss as persistent, random events rather than the bursts of packet
loss that actual WANs experience. Thus, if you are testing with one of these WAN emulators, you will also
observe this artificially lower user experience.
The best solution to this problem is to find and fix the source of packet loss in the network (or use a more
sophisticated WAN emulator). While the network packet loss issue is being resolved, the PCoIP session
experience can be improved by using the Device Bandwidth Floor setting (see Section 3.1.2)
Note that misuse of the Device Bandwidth Floor can also create packet loss. If the combined “floor bandwidth”
of multiple PCoIP sessions on the same network exceeds the capacity of that network, the PCoIP protocol will
attempt to transmit more data than the network can accommodate, resulting in continuous packet loss. To
prevent this, ensure your network can provide the combined floor bandwidth for all the sessions sharing a
common network link and adjust session floor bandwidths (or network capacity) if necessary.
3.5 Packet Reordering
The PCoIP protocol is capable of handling packets that arrive in a dierent order from that in which they were
sent because a small amount of packet reordering can be expected in a WAN. However, if a packet does not
arrive within a certain time window, it is considered “lost” by the PCoIP protocol even though it may eventually
arrive. This is done to preserve the interactivity of the user experience: in a dynamic environment, significantly
delayed packets are often no longer relevant. However, if the network is consistently delivering packets “late,”
the experience will be similar to a network with persistent packet loss.
Thus, if your PCoIP sessions are consistently operating at the “floor bandwidth” even though the network is not
congested and no significant packet loss is being reported, packet reordering may be the cause. A device in
the network path (e.g., a router or WAN accelerator) is the likely source of persistent packet reordering. While
the source is being identified and fixed, the PCoIP session experience can be improved by raising the Device
Bandwidth Floor setting (see Section 3.1.2).
3.6 Auto-Discovery and Subnets
Many PCoIP zero clients ship with auto-discovery turned on by default. This feature locates PCoIP host cards
on the same subnet as the client and is intended primarily for test rather than production use. Use of DNS-SRV
records is recommended for production deployments.
For production deployments, or if your host and client are on dierent subnets, disable auto-discovery via
Configuration Discovery on the zero client OSD or Web interface and configure the session information
manually by entering the IP address (or FQDN) and MAC address of the peer host card under Configuration
Session in the zero client Web interface or zero client OSD (see Figures 7, 8, 9, 10). The host card MAC address
is printed on a sticker on the card itself and on the box of most host cards.
