wiki:QoS

Context Navigation

Version 2 (modified by bennylp, 15 years ago) (diff)
--

Support for QoS (TOS/DSCP, WMM, 802.1p)

Table of Contents

Introduction on QoS
Availability
Objective
Design
1. Portable High Level API
2. Fine Grained Control API
Limitations
References

This article describes the QoS support in PJSIP and how to use it.

Introduction on QoS

QoS settings are available for both Layer 2 and Layer 3 of TCP/IP protocols:

Layer 2: IEEE 802.1p for Ethernet

IEEE 802.1p tagging will mark frames sent by a host for prioritized delivery using a 3-bit Priority field in the virtual local area network (VLAN) header of the Ethernet frame. The VLAN header is placed inside the Ethernet header, between the Source Address field and either the Length field (for an IEEE 802.3 frame) or the EtherType field (for an Ethernet II frame).

Layer 2: WMM

At the Network Interface layer for IEEE 802.11 wireless, the Wi-Fi Alliance certification for Wi-Fi Multimedia (WMM) defines four access categories for prioritizing network traffic. These access categories are (in order of highest to lowest priority) voice, video, best-effort, and background. Host support for WMM prioritization requires that both wireless network adapters and their drivers support WMM. Wireless access points (APs) must have WMM enabled.

Layer 3: DSCP

At the Internet layer, you can use Differentiated Services/Diffserv? and set the value of the Differentiated Services Code Point (DSCP) in the IP header. As defined in RFC 2472, the DSCP value is the high-order 6 bits of the IP version 4 (IPv4) TOS field and the IP version 6 (IPv6) Traffic Class field.

Layer 3: Other

Other mechanisms exist (such as RSVP, IntServ) but this will not be implemented.

Availability

Linux

DSCP is available via IP TOS option.

Ethernet 802.1p tagging is done by setting setsockopt(SO_PRIORITY) option of the socket, then with the set_egress_map option of the vconfig utility to convert this to set vlan-qos field of the packet.

WMM is not known to be available.

MacOS X

DSCP is available via IP TOS option.

Windows and Windows Mobile

(It's a mess!)

DSCP is settable with setsockopt() on Windows 2000 or older, but Windows would silently ignore this call on WinXP or later, unless administrator modifies the registry. On Windows 2000, Windows XP, and Windows Server 2003, GQoS (Generic QoS) API is the standard API, but this API may not be supported in the future. On Vista and Windows 7, the is a new QoS2 API, also known as Quality Windows Audio-Video Experience (qWAVE).

IEEE 802.1p tagging is available via Traffic Control (TC) API, available on Windows XP SP2, but this needs administrator access. For Vista and later, it's in qWAVE.

WMM is available for mobile platforms on Windows Mobile 6 platform and Windows Embedded CE 6, via setsockopt(IP_DSCP_TRAFFIC_TYPE). qWAVE supports this as well.

Symbian S60 3rd Ed

Both DSCP and WMM is supported via RSocket::SetOpt() with will set both Layer 2 and Layer 3 QoS settings accordingly.

Summary

The following table summarizes the availability/accessability of various QoS settings on platforms that PJSIP supports:

	Win2k/older	XP, Vista, WM2003, WM5	WM6	Symbian S60	Linux	MacOS X	iPhone
High level API	Yes	No	Yes	Yes	Yes	Yes	Yes
API backend	qos_bsd.c	qos_dummy.c	qos_wm.c	qos_symbian.cpp	qos_bsd.c	qos_bsd.c	qos_bsd.c
DSCP is supported	Yes	No	Yes	Yes	Yes	Yes	Yes
DSCP is user settable	Yes	No	No	Yes	Yes	Yes	Yes
WMM prio is supported	No	No	Yes	Yes	No	No	No
WMM prio is user settable	No	No	No	No	No	No	No
SO_PRIORITY is supported	No	No	No	No	Yes	Yes	Yes
SO_PRIORITY is settable	No	No	No	No	Yes	Yes	Yes

Objective

The objective of this ticket is to add new API to PJLIB socket API to enable manipulation of the QoS parameters above in a uniform and portable manner.

Design

Based on the above, the following API is proposed.

Declare the following "standard" traffic types.

typedef enum pj_qos_type
{
   PJ_QOS_TYPE_BEST_EFFORT,
   PJ_QOS_TYPE_BACKGROUND,
   PJ_QOS_TYPE_VIDEO,
   PJ_QOS_TYPE_VOICE,
   PJ_QOS_TYPE_CONTROL
} pj_qos_type;

The traffic classes above will determine how the Layer 2 and 3 QoS settings will be used. The standard mapping between the classes above to the corresponding Layer 2 and 3 settings are as follows:

PJLIB Traffic Type IP DSCP WMM 802.1p
BEST_EFFORT 0x00 BE (Bulk Effort) 0
BACKGROUND 0x08 BK (Bulk) 2
VIDEO 0x28 VI (Video) 5
VOICE 0x30 VO (Voice) 6
CONTROL 0x38 VO (Voice) 7

There are two sets of API provided to manipulate the QoS parameters.

Portable High Level API

The first set of API is:

// Set QoS parameters
PJ_DECL(pj_status_t) pj_sock_set_qos_type(pj_sock_t sock,
                                          pj_qos_type val);

// Get QoS parameters
PJ_DECL(pj_status_t) pj_sock_get_qos_type(pj_sock_t sock,
                                          pj_qos_type *p_val);

The API will set the traffic type according to the DSCP class, for both Layer 2 and Layer 3 QoS settings, where it's available. If any of the layer QoS setting is not settable, the API will silently ignore it. If both layers are not setable, the API will return error.

The API above is the recommended use of QoS, since it is the most portable across all platforms.

Fine Grained Control API

The second set of API is intended for application that wants to fine tune the QoS parameters.

The Layer 2 and 3 QoS parameters are stored in pj_qos_params structure:

typedef enum pj_qos_flag
{
   PJ_QOS_PARAM_HAS_DSCP = 1,
   PJ_QOS_PARAM_HAS_802_1_P = 2,
   PJ_QOS_PARAM_HAS_WMM = 4
} pj_qos_flag;

typedef enum pj_qos_wmm_prio
{
   PJ_QOS_WMM_TYPE_BULK_EFFORT_PRIO,
   PJ_QOS_WMM_TYPE_BULK_PRIO,
   PJ_QOS_WMM_TYPE_VIDEO_PRIO,
   PJ_QOS_WMM_TYPE_VOICE_PRIO
} pj_qos_wmm_prio;

typedef struct pj_qos_params
{
   pj_uint8_t      flags;    // Determines which values to 
                             // set, bitmask of pj_qos_flag
   pj_uint8_t      dscp_val; // DSCP value to set
   pj_uint8_t      so_prio;  // SO_PRIORITY value
   pj_qos_wmm_prio wmm_prio; // WMM priority value
} pj_qos_params;

The second set of API with more fine-grained control over the parameters are:

// Retrieve QoS params for the specified traffic type
PJ_DECL(pj_status_t) pj_qos_get_params(pj_qos_type type, 
                                       pj_qos_params *p);

// Set QoS parameters to the socket
PJ_DECL(pj_status_t) pj_sock_set_qos_params(pj_sock_t sock,
                                            const pj_qos_params *p);

// Get QoS parameters from the socket
PJ_DECL(pj_status_t) pj_sock_get_qos_params(pj_sock_t sock,
                                            pj_qos_params *p);

Important:

The pj_sock_set/get_qos_params() APIs are not portable, and it's probably only going to be implemented on Linux. Application should always try to use pj_sock_set_qos_type() instead.

PJLIB Traffic Type	IP DSCP	WMM	802.1p
BEST_EFFORT	0x00	BE (Bulk Effort)	0
BACKGROUND	0x08	BK (Bulk)	2
VIDEO	0x28	VI (Video)	5
VOICE	0x30	VO (Voice)	6
CONTROL	0x38	VO (Voice)	7